615 FXUS64 KFWD 020259 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 859 PM CST Tue Jan 1 2019 .UPDATE... The 00z FWD sounding shows a pretty substantial sub-freezing layer just above the surface in the lowest 3000 feet with coldest temps down to about -4C. The NAM forecasted this type of profile and the other models are a bit warmer which means we are liking the NAM output through Wednesday the best. The issue that we are wrestling with is that if precipitation originates in this layer it would be drizzle due to the very shallow region of lift below the frontal inversion, and it would also be supercooled - meaning that it will be more effective at coating elevated objects with a glaze of ice if it's substantial enough. We are within the time range where we can slice the onion pretty thin and it appears that temperatures near or just below freezing will occur in northwestern and western Tarrant county and western Johnson county where the terrain is just a little bit higher. The current wet bulb temperatures (representing how cold actual temperatures could fall via evaporational cooling) are already at 32F and expected to fall another degree by sunrise in this area. The numerous bridges and overpasses (and some of the flyovers reach 100 feet above the surface where temps will be even cooler) makes us a little more wary of the traffic impacts of even a trace of icing could have. So we will be adding Tarrant and Johnson counties to the winter weather advisory as we believe that those commuting on the bridges and overpasses in the morning should be wary of icy spots and probably need to adjust their daily routine - whether that means just adding more time for their commute or choosing a route that doesn't involve a high bridge or interchange. Once the true rain reaches the area (that is forming higher up in and a much warmer part of the atmosphere) we expect that surface temperatures will warm above freezing. These rain drops will be above freezing and would even serve to help melt any ice that did collect. Thus the 2 county addition to the winter weather advisory will only be from 3 am to noon. Plain old cold rain is expected for the afternoon hours. It must be stressed that we are talking about very light amounts of icing and only on elevated surfaces, and essentially the forecasted meteorological variables are hardly changed from the previous forecast. What we're trying to forecast here are the impacts of those variables on society (weather is hard enough, but impacts are another layer of uncertainty). Regardless we've seen enough in the current data to make us concerned that the weather could cause a disruption in parts of Tarrant and Johnson counties. The remainder of the forecast remains unchanged. TR.92 && .AVIATION... /Issued 554 PM CST Tue Jan 1 2019/ Obviously the main concern will be the potential for light freezing precipitation Wednesday morning in the Metroplex. Regardless of the exact temperature, it will be cold enough when precipitation is occurring for de-icing operations for any arriving flights for cold soaked wings. Regarding the specific meteorological forecast, have included a mention of freezing drizzle at AFW and FTW from 13z-17z Wed morning where temperatures will likely be near or just below freezing. At the other TAF sites it appears temps will be just above freezing, but DFW is a very close call. Precipitation will develop over the region around sunrise and during the first few hours of its arrival is the primary time of concern for possible icing. As rain coverage and intensity increases during the mid to late morning hours, this will bring warmer air to the surface and temps will get above freezing at all TAF sites for an all liquid precipitation. For CIGs, a wedge of low level dry air is moving into the Metroplex from the northeast, and CIGs are working above 2000 feet and even scattering out to VFR at a couple of sites. Believe with sunset we'll see these CIGs fill back below 2000 feet in a couple hours and gradually fall through the night. Once rain begins low level saturation will occur and likely result in IFR CIGs and possibly MVFR visibilities Wednesday afternoon/evening. Have carried light rain through the day Wednesday even though it will likely not be continuous. Otherwise north winds will prevail near 10 knots. TR.92 && .DISCUSSION... /Issued 331 PM CST Tue Jan 1 2019/ A complex forecast for the next few days. Here are the main takeaways: 1. Winter Weather Advisory remains in effect beginning late tonight for locations along and west of a line from Dennison to Denton to Glen Rose to Goldthwaite. 2. Rain will begin in the south tonight with light freezing rain possible across the west before sunrise Wednesday. 3. A mix of rain/light freezing rain across Advisory area Wednesday/Wednesday night. Mainly cold rain elsewhere with isolated thunderstorms and locally heavy rain southeast. 4. A winter mix (Freezing Rain/Sleet/Snow) possible Thursday generally north of I-20. No significant accumulations or impacts outside the advisory area. 5. Accumulations across the Advisory area: Ice: 1/10-2/10 inch. Snow <=1 inch. 6.Precipitation ends before sunrise Friday. Tonight... Extensive post frontal stratus and continued cold air advection has kept temperatures in the 30s and 40s across most of North and Central Texas this afternoon except for some upper 20s in the west and lower 50s in the extreme southeast. This cold air will remain in place at the surface tonight while moisture steadily increases above it. A few light showers will develop across Central Texas during the evening as isentropic ascent increases. Precipitation will increase overnight as an upper low deepens across southern Arizona and New Mexico. The best lift, moisture and instability will remain across Central and South Texas, thus we will maintain high PoPs and mention isolated thunderstorms. A sharp southeast to northwest moisture and temperature gradient will exist as we head into the overnight hours with locations across the northwest half of the forecast area likely below freezing. The good news is that precipitation in the subfreezing air will be light and limited to mainly locations south of I-20 and near and west of US 281. However, some light freezing rain and travel impacts could begin across the southwest counties of the Advisory area in the predawn hours. Wednesday... Periods of precipitation are still expected on Wednesday as the upper low moves into far West Texas. It still appears that the best rain chances will be across the southeast zones where some locally heavy rainfall and isolated thunderstorms will be possible (temps stay above freezing). Farther to the northwest (current Winter Weather Advisory Area) subfreezing temperatures to start the day will result in periods of light freezing rain with some light ice accumulations possible. Temperatures during the day Wednesday should warm a few degrees as low level cold air advection wanes. However, a few of the north/northwest zones could still hover near freezing so a light rain/freezing rain mix is possible even through the afternoon. The slightly warming temperatures expected Wednesday afternoon should result in a lull in travel impacts across the advisory area but this will need to be monitored closely. It is also possible that some areas just outside of the advisory area could see temperatures at or just below freezing for part of the day Wednesday with some light freezing rain on elevated surfaces. However, travel impacts are not anticipated since surface temperatures are unlikely to fall below 30 degrees. Wednesday night... The upper low is progged to move across West Texas Wednesday night. There will likely be a lull in precipitation during the early evening hours but precipitation should ramp up mid to late evening as large scale forcing increases. Models are in fairly good agreement on the placement of the upper low and best forcing as we head into the overnight hours. We expect an uptick in precipitation across the Big Country and Low Rolling Plains shortly after midnight with the heavier precipitation moving into the western zones before sunrise. Although a mix of rain/freezing rain will be most likely across the Advisory area for most of the night, a transition to sleet and snow is looking more likely as we head towards sunrise due to dynamic cooling. Precipitation across the rest of the region should remain all liquid with temperatures generally above freezing. Once again, a few spots on the fringes of the Advisory may see some light freezing rain, but impacts are not expected since surface temperatures should remain above 30 degrees. Thursday/Thursday night... Thursday could be an interesting day as the upper low tracks through the heart of the forecast area. Although much of the region will be above freezing through the day, lift will be maximized as the low churns eastward, resulting in some cooling aloft, a transition of precipitation type, and some pockets of heavier precipitation. The northwest zones will have the best chance of seeing a transition to all snow while surface temperatures are still below freezing Thursday morning. Therefore, some light accumulating snow is possible (generally 1 inch or less). There is still an outside chance of some locally higher snow amounts, but it is too difficult this far out to forecast where a convective snow band might develop. Locations east of the Advisory area (including the immediate Dallas/Fort Worth Metroplex) may also experience a rain/snow mix Thursday as the upper low moves overhead, but impacts from this precipitation appear minimal at this time due to the expected surface temperature. We do anticipate a dryslot to move in from the southwest as the upper low translates east across the region which should bring a rapid end to the precipitation from southwest to northeast through the afternoon/evening with all precipitation exiting to the northeast before sunrise Friday. Upper level high pressure will build in from the west on Friday, resulting in a steady warmup. The upper ridge axis will move east of the region on Sunday while a shortwave moves in from the west. This approaching trough will bring Gulf moisture back to the region along with a chance for showers Sunday night and Monday. The trough will move through the region Monday night with drier and slightly cooler air expected Tuesday. 79 && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 33 37 33 38 32 / 20 60 60 60 30 Waco 36 38 35 41 32 / 50 90 60 50 10 Paris 34 37 32 42 33 / 20 80 60 70 40 Denton 31 35 30 36 31 / 20 60 60 60 40 McKinney 32 37 32 38 32 / 20 60 60 70 40 Dallas 34 38 34 39 33 / 20 70 60 60 30 Terrell 35 40 35 42 32 / 40 90 70 60 20 Corsicana 37 41 36 42 32 / 60 90 70 60 20 Temple 35 38 34 43 33 / 60 90 70 40 10 Mineral Wells 30 35 30 37 30 / 20 60 60 60 20 && .FWD WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 AM to noon CST Wednesday for TXZ118-133. Winter Weather Advisory from 3 AM Wednesday to 6 AM CST Friday for TXZ091>093-100>103-115>117. Winter Weather Advisory from 3 AM Wednesday to noon CST Thursday for TXZ129>132-141>143. && $$